The initial classification of adrenergic receptors into α- and β-families was first described by Ahlquist in 1948 (Ahlquist RP, “A Study of the Adrenergic Receptors,” Am. J. Physiol. 153:586-600 (1948)). Functionally, the α-adrenergic receptors were shown to be associated with most of the excitatory functions (vasoconstriction, stimulation of the uterus and pupil dilation) and B-adrenergic receptors were implicated in vasodilation, bronchodilation and myocardial stimulation (Lands et al., “Differentiation of Receptor Systems Activated by Sympathomimetic amines,” Nature 214:597-598 (1967)). Since this early work, α-adrenergic receptors have been subdivided into α1- and α2-adrenergic receptors. Cloning and expression of α-adrenergic receptors have confirmed the presence of multiple subtypes of both α1-(α1A, α1B, α1D) and α2-(α2A, α2B, α2C) adrenergic receptors (Michel et al., “Classification of α1-Adrenoceptor Subtypes,” Naunyn-Schmiedeberg's Arch. Pharmacol, 352:1-10 (1995); Macdonald et al., “Gene Targeting—Homing in on α2-Adrenoceptor-Subtype Function,” TIPS, 18:211-219 (1997)).
Current therapeutic uses of α2 adrenergic receptor drugs involve the ability of those drugs to mediate many of the physiological actions of the endogenous catecholamines. There are many drugs that act on these receptors to control hypertension, intraocular pressure, eye reddening and nasal congestion and induce analgesia and anesthesia.
α2 adrenergic receptors can be found in the rostral ventrolateral medulla, and are known to respond to the neurotransmitter norepinephrine and the antihypertensive drug clonidine to decrease sympathetic outflow and reduce arterial blood pressure (Bousquet et al., “Role of the Ventral Surface of the Brain Stem in the Hypothesive Action of Clonidine,” Eur. J. Pharmacol., 34:151-156 (1975); Bousquet et al., “Imidazoline Receptors: From Basic Concepts to Recent Developments,” 26:S1-S6 (1995)). Clonidine and other imidazolines also bind to imidazoline receptors (formerly called imidazoline-guanidinium receptive sites or IGRS) (Bousquet et al., “Imidazoline Receptors: From Basic Concepts to Recent Developments,” 26:S1-S6 (1995)). Some researchers have speculated that the central and peripheral effects of imidazolines as hypotensive agents may be related to imidazoline receptors (Bousquet et al., “Imidazoline Receptors: From Basic Concepts to Recent Developments,” 26:S1-S6 (1995); Reis et al., “The Imidazoline Receptor: Pharmacology, Functions, Ligands, and Relevance to Biology and Medicine,” Ann. N.Y. Acad. Sci., 763:1-703 (1995).
Compounds which have adrenergic activity are well known in the art, and are described in numerous patents and scientific publications. The two main families of adrenergic receptor are termed alpha adrenergic receptors and beta adrenergic receptors in the art, and each of these two families is known to have subtypes, which are designated by letters of the alphabet, such as α2A, α2B, and α2C. It is generally known that adrenergic activity is useful for treating animals of the mammalian species, including humans, for curing or alleviating the symptoms and conditions of numerous diseases and conditions. In other words, it is generally accepted in the art that pharmaceutical compositions having an adrenergic compound or compounds as the active ingredient are useful for treating, among other things, glaucoma, chronic pain, migraines, heart failure, and psychotic disorders. It is also known that compounds having adrenergic activity, such as α2A agonists, may be associated with undesirable side effects. Examples of such side effects include hyper- and hypotension, sedation, locomotor activity, and body temperature variations.
It has been discovered in accordance with the present invention that adrenergic compounds that act selectively, and preferably even specifically, as agonists of the α2C or the α2B/α2C (hereinafter referred to as α2C or α2B/2C) receptor subtypes in preference over the α2A receptor subtype, with adrenergic compounds that are functionally selective agonists of the α2C receptor subtype in preference over the α2A receptor subtype and α2B/2C receptor subtype, possess desirable therapeutic properties associated with adrenergic receptors but without having one or more undesirable side effects such as changes in blood pressure (e.g., a hypertensive or hypotensive effect) or sedation. For the purposes of this present invention, a compound is defined to be an active agonist of the α2C receptor subtype if the compound's efficacy at the α2C receptor is ≧30% Emax (GTPγS assay). A compound is a functionally selective agonist of the α2C receptor subtype over the α2A receptor subtype if the compound's efficacy at the α2C receptor is ≧30% Emax (GTPγS assay) and its efficacy at the α2A receptor is ≦30% Emax (GTPγS assay).
There is a need for new compounds, formulations, treatments and therapies to treat diseases and disorders associated with α2C adrenergic receptors. Furthermore, there is a need to develop compounds that are functionally selective for the α2C receptor subtype with respect to the α2A receptor subtype or the α2B/α2C receptor subtype. It is, therefore, an object of this invention to provide compounds useful in the treatment or prevention or amelioration of such diseases and disorders.